Nasal mask



FIG. 1 is a front perspective view of a nasal mask according to our design;

FIG. 2 is a front view thereof; and,

FIG. 3 is a left side view thereof, with the right side view being a mirror image thereof.

Where included, broken lines showing environment or structure are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a nasal mask, as shown and described. 